DNA replication models – Which hypothesis correctly describes how DNA replicates in cells?

Introduction:
The mechanism of DNA replication was a central question resolved by the Meselson–Stahl experiment. Understanding the difference between conservative, semi-conservative, and dispersive models is essential for interpreting replication intermediates and isotope-labeling outcomes.

Given Data / Assumptions:

• Each DNA duplex contains two antiparallel strands.
• Replication requires templated synthesis.
• Isotopic labeling can distinguish old from newly synthesized DNA based on density.

Concept / Approach:
In semi-conservative replication, each daughter duplex contains one parental (old) strand and one newly synthesized strand. After one round of replication in 14N medium following 15N labeling, all DNA becomes hybrid density; after the second round, two bands (hybrid and light) appear—patterns inconsistent with purely conservative or purely dispersive models.

Step-by-Step Solution:

Verification / Alternative check:
Pulse–chase experiments and visualization of replication forks also corroborate strand-separation mechanisms consistent with semi-conservative copying.

Why Other Options Are Wrong:

• Conservative: predicts distinct heavy and light bands after one round, not observed.
• Dispersive: predicts a single intermediate band that shifts each generation, not observed.
• Evolutionary or hybrid theories: not accepted replication mechanisms.

Common Pitfalls:
Confusing band patterns after first versus second replication cycles; semi-conservative yields hybrid after one, hybrid + light after two.

Final Answer:
Semi-conservative replication theory